1. Field of the Invention
The present invention relates generally to heat exchangers, and more particularly, but not by way of limitation, to a heat exchanger for use in a closed loop cooling system for a marine engine.
2. Description of the Prior Art
Many marine engines, particularly those designed for use in salt water, utilize closed loop cooling systems. In a closed loop cooling system, a cooling fluid stream circulates through the engine and also through the shell side of a shell and tube heat exchanger. Raw water from an ocean or lake is pumped in a raw water stream through the tube side of the heat exchanger, so that excess heat from the marine engine is transferred from the closed loop cooling fluid stream to the raw water stream in the heat exchanger. The raw water stream then returns the excess heat to the ocean or lake. Thus, raw water, especially salt water, never passes through the cooling fluid passages of the engine. Also, antifreeze and other such coolant fluids can be used in the closed loop cooling fluid stream.
Such heat exchangers for use in closed loop cooling systems of marine engines have in the past been constructed substantially entirely of copper. The outer shell, end plates, and tubes were all copper and were brazed together.
Although copper heat exchangers such as that just described have been successfully utilized in closed loop cooling systems for marine engines by the assignee of the present invention and by others for many years, there are several disadvantages inherent in this prior design.
The heat exchangers constructed from copper are relatively expensive due to the cost of materials and the substantial amount of labor required for construction of the soldered assembly. Additionally, the copper shells are subject to physical damage when being handled prior to installation in a marine vessel. The thin copper shells are relatively easy to dent, and such dented units typically must be scrapped since they are aesthetically unacceptable for sale as a new item. Additionally, heat exchangers constructed of copper are subject to substantial corrosion problems, particularly in salt water. Further, since the tube bundle cannot be readily removed from the shell with a heat exchanger constructed of brazed copper, any leaking tubes must simply be plugged, thus reducing the overall effectiveness of the heat exchanger.